This study will make contributions to a very under-researched topic of infant cognitive development by examining how various factors affect the direction and degree of adrenocortical response in young infants in learning situations. Cortisol, an adrenal steroid hormone, is secreted in response to physical and emotional stress and is also associated with high states of arousal. Our previous research showed that those infants who exhibited declining cortisol during a maternal separation/learning event showed learning and memory for the target stimuli. A link between declining cortisol reactivity and better learning/memory was the expected outcome given the argument that the control of both emotion and cognitive processes resides in common brain areas. However, our previous results were inconsistent with some other investigations of the relationship between adrenocortical and infant cognitive functioning. The primary aim of the proposed experiments is to ascertain the nature of the differential results across studies by exploring several factors hypothesized to affect the direction of cortisol reactivity during learning events, including physiological activity, socioemotional distress, and maternal efforts to assist infant emotional regulation. Two short longitudinal studies are planned. Data will be collected on mother-infant pairs at these infant ages: 2 months, 3 months, and 6 months. Salivary cortisol samples will be taken from the infant and the mother to assess the direction and degree of cortisol reactivity to a separation/learning event. Infants will participate in four experiments, designed to assess various aspects of infant learning and memory for language and voice stimuli. In a second set of experiments, mothers will be trained to exhibit behaviors intended to assist their infants in regulating their adrenocortical response patterns. It is predicted that this maternal sensitivity training will promote better learning and memory in infants. Behavioral synchrony will be measured by observing specific behaviors of the mother and infant in 10-sec intervals across a short interaction period. We will continue to investigate these relationships in a population that is underrepresented in the related literature. The research will add valuable data to the literature on the relationship between cognitive processing in infancy, adrenocortical functioning in mothers and infants, and sensitivity of the caregiver to the infant.